People have long been fascinated with structures and forms which are easily collapsible and/or readily expandable. A pioneer in this field is Chuck Hoberman, now affiliated with Hoberman Associates. Hoberman holds several U.S. patents relating to ‘reversibly expandable structures,’ including radially expanding trusses. Hoberman's initial patents dealt with transformability in structures. In 2008, Hoberman founded Adaptive Building Initiative with Buro Happold to design rapidly transformable buildings, which led to the construction of the POLA Ginza Building's adaptive façade in 2009. Three more of Hoberman's adaptive shading installations were constructed in 2010, including the Aldar Central Market, the Wyss Institute at Harvard, and the Simons Center at Stony Brook University.
Johnson Outdoors of Racine, Wis., a manufacturer of tents for both government and consumer markets, approached Hoberman Associates in 2005 to develop a new line of large shelters for military use and crisis relief. This led to the development of Rapidly Deployable Shelters (RDS) under Johnson's Eureka brand. With easier deployment and minimal time-consuming secondary connections, the RDS system uses fewer, larger, and more robust parts than competitive products. The RDS comes in several sizes, the largest of which deploys to 750 square feet, and folds down to a 3 foot by 3½ foot by 6 foot compact bundle.
U.S. Pat. No. 7,644,721 to Hoberman et al. is directed to tents and the provision of temporary shelter. The particular problem addressed in the patent relates to extensible tong linkages, sometimes referred to as scissor linkages which are used to construct transformable truss-structures in a variety of shapes. While such scissor linkages are effective in creating structures that deploy or transform, once the structure is deployed, they are less effective in providing an optimum structural system. This is due to the fact that the “structural depth” of a scissor linkage varies widely. In some places, there is significant distance between its links while in other places, both links overlap such that there is no depth provided beyond the individual link dimensions. This results in a basic structural inefficiency. Such inefficiency can limit the structural span, lead to increased weight, and prevent efficient packaging.
The '721 patent describes a system based on parallel, four-bar linkages. The invention relates to means of connecting series of four-bar linkages together such that they provide a structural truss in their extended state, provide a compact package in their retracted state, and move together in a synchronized fashion. The mechanism is comprised of two or more four-bar linkages wherein each linkage shares a common link with each adjacent linkage and the movement of said two or more linkages is synchronized by mechanical means such that said mechanism may move between a collapsed and an extended state. The mechanical means may be in the form of additional links or geared connections. The patent further discloses means to cause the mechanism, when in its extended state, to become stiff and structural. Fabric elements may be attached to these mechanisms to form rapidly deployable shelters.
Another commercially available rapidly deployable shelter is called DRASH (Deployable Rapid Assembly Shelter), a portable, geodesic shelter that can be set up within minutes of arriving on site with no special tools. The system is manufactured and sold by DHS Systems LLC (Orangeburg, N.Y.). The structures, which are supported by composite struts, have footprints from 109 sq ft (10.1 m2) up to 1,250 sq ft (116 m2). Each DRASH shelter comes with flooring and ground covers manufactured from polyester and nylon to U.S. military standards. DRASH also provides generators and trailers plus various accessories for the shelters themselves. For transport or storage, the shelters pack down to less than 2% of its deployed size into a transport bag that can be stowed on a trailer or HMMWV. Teams of four to six can easily erect a shelter simply by pulling on the sides of the shelter and raising the shelter in designated “push points” on the shelter.
The above examples are only a few of many more in the field of rapidly deployable structures, shelters, tents and other temporary or emergency dwellings. Other examples include, for example, inflatable components.
Commonly assigned U.S. Pat. No. 7,910,193, relates to negative Poisson's ratio (NPR) or auxetic structures and, in particular, to three-dimensional auxetic structures and applications thereof. Poisson's ratio (ν), named after Simeon Poisson, is the ratio of the relative contraction strain, or transverse strain (normal to the applied load), divided by the relative extension strain, or axial strain (in the direction of the applied load). Some materials, called auxetic materials, have a negative Poisson's ratio (NPR). If such materials are stretched (or compressed) in one direction, they become thicker (or thinner) in perpendicular directions.
NPR structures can react differently under applied loads. One possibility is a reactive shrinking mechanism, obtained through a topology optimization process. The unique property of this structure is that it will shrink in two directions if compressed in one direction. Auxetic and NPR structures have been used in a variety of applications. Heretofore, however, such structures have not been exploited for use in rapidly deployable shelters and components used in such structures.